1. Field of the Invention
The invention relates to captive panel fastener assemblies; and, more particularly, to an improved captive panel fastener assembly for improved retention and locking of aircraft panels or the like.
2. Description of the Prior Art
Panel fasteners for aircraft are well known in the art. These fasteners secure the panel of an aircraft to a sub-panel by insertion through an opening in the panel with the fastener threadably engaging a receptacle assembly mounted on the sub-panel. The enlarged head of the fastener abuts against the panel on the access side and means known in the prior art are provided for preventing the fastener from becoming disengaged from the panel when the fastener is threaded out of engagement with the receptacle assembly.
One type of such panel fasteners include a stud assembly mounted to a sub-panel, under-structure or substructure through a basket, which assembly includes an axially extending male threaded stud held in place by a barrel mounted to the basket. The internal threads of the panel fastener engage the threads of the stud and clamp the the top panel and sub-panel together.
Various means have been suggested in the art to hold the panel fastener to the panel prior to engagement with the receptacle assembly. In certain applications, the panels may be made of composite materials and such materials may be easily cracked or delaminated if the load on the panel fastener assembly is not distributed over the area surrounding the hole.
In U.S. Pat. No. 4,285,380 to Gulistan, a panel fastener is disclosed having a stud nut with an internally threaded bore mounted to a grommet assembly installed in a panel. The nut is adapted to threadably engage a threaded nut mounted to a subpanel. In one position, the nut is held outwardly away from the panel by a retaining ring in the grommet assembly trapped in a groove adjacent the nose of the nut. When the nut is pushed inwardly of the panel, the retaining ring in the grommet assembly rides over the shank of the nut until it abuts against the nut head thereby holding the nut to the panel in an inward position until the nut is pulled away from the panel. The ring then rides along the nut shank until it re-enters the groove adjacent the nose of the nut.
Obviously, the grommet assembly of Glistan requires carefully machined parts and a relatively thick panel 16 for installation. Gulistan also requires a rather intricate hole to be formed in the panel for the grommet assembly.
In U.S. Pat. No. 4,324,517 to Dey, a panel fastener assembly is disclosed for joining a panel to a sub-panel. This assembly shows a nut having an internal thread fixed to a grommet assembly installed in the panel. A receptable assembly is attached to the sub panel. The grommet assembly has a retainer ring which engages a groove in the nut body when the nut is in the outwardly extended or withdrawn position and disengaged from the receptacle assembly. As can be seen in FIGS. 5 and 8 of Dey, carefully machined parts make up the panel fastener assembly. Further, as can be seen in FIG. 1 of Dey, a relatively thick panel 4 is required for installation of the grommet assembly.
Thus, in both Gulistan and Dey, parts are required which must be carefully machined and sub-assembled. The sub-assemblies require a relatively thick panel for installation and add weight to the installation. Certain panels, such as car door panels and the like, must be relatively thin and are light in weight. Thus, any fastener assemblies used in such panels must be very small and light weight. The installations of Gulistan and Dey are thick and heavy and add to the weight of the installation. This is highly undesirable, particularly in aircraft installations where it increases the payload of the aircraft. The grommets of both Dey and Gulistan do not provide a very large bearing surface where the bottom portions engage and bear against the panel. Further, panel thicknesses vary and it may be difficult to swage the grommets of Dey and Gulistan to hold the same in position in the panels. In addition, in both Dey and Gulistan, the grommets are installed by flaring the grommet on the exposed or access or exterior side of the panel. This assembly does not ensure an aerodynamically flush surface.
These type of fasteners are used on aircraft access doors and, in the prior art devices heretofore discussed, the grommets thereof must be swedged into the countersink on the exterior side of the door panel. Since door panel thicknesses vary, the grommet swedged portion may protrude either above the door panel or considerably lower than the door panel creating a potential aerodynamic problem. There is a need for a grommet head that ensures a consistent flushness on the exposed side of the door panel. That is, there is a need for a grommet assembly that tolerance resulting in varying thicknesses of door panels is taken up on the assembly itself. There is also a need for a grommet which has an internal cavity for the retaining ring of the bolt wherein the cavity is disposed between the access side and the blind side of the panel and thus not exposed so that it can be damaged which would affect the functioning thereof.
Further, as heretofore discussed, new aircraft designs use lightweight materials, such as composites. Doors of such material are easily damaged. Prior art devices must be swedged directly into the composite door resulting in possible damage to the door. There is a need for a grommet assembly that can be installed in an aircraft access door without damage thereto during such installation.
There is thus a need for a panel fastener assembly that can always be swaged uniformly against the panel in which the fastener is installed regardless of the thickness of the panel. Such an assembly should be able to secure a panel to a sub-panel where the bolt thereof may be held in a withdrawn or outward position without disengagement from the panel until it engages a receptacle assembly, on the subpanel. Such a fastener assembly should be lightweight, be easily manufactured and installed yet provide strength and rigidity to the installation.
In copending application Ser. No. 06/912,796, filed Sept. 26, 1986, now U.S. Pat. No. 4,735,536, issued Apr. 5, 1988, entitled "Captive Panel Fastener Assembly and Method For Installing the Same", John Duran, inventor, and commonly assigned, there is described a captive panel fastener assembly and method for installing the same wherein the fastener has a grommet with a cavity trapping a retaining ring therein, the cavity being generally rectangular in cross section Although it is highly unlikely, it is possible that repeated and intentional wiggling, twisting and bending of the bolt might result in the bolt coming out of the grommet. There thus is a need for a panel fastener wherein the bolt cannot come out of the grommet even if one wiggled, twisted and bent the bolt in the grommet.